Production of off-grade polycarbonate batches can occur in even well-designed and well-run plants. It is often not feasible to dispose of the sub-grade polymer by blending it with better grade material. Consequently, unless some method of salvaging the off-grade material can be devised, a substantial waste of both resources and money results.
U.S. Pat. No. 3,223,678 is directed to a method of reducing the length of polycarbonate molecules otherwise unsuited for use in lacquers capable of forming "dry-bright" coatings. The polycarbonate is reacted with morpholine or monoethanolamine, thereby producing a corresponding carbamate-terminated polycarbonate in which the average chain length has been shortened in proportion to the amine to carbonate-moiety ratio employed.
Although amine to polycarbonate ratios high enough to result in cleavage of up to about 80% of the carbonate groups are claimed, nothing is disclosed suggesting that degrading so much of the polymer chain, rather than selecting a lower molecular weight polycarbonate to start with, would be seriously contemplated.
The patent is silent as to the character of the non-polymeric co-products, but it is apparent that the co-products derived from morpholine would not be difunctional and could not be utilized as monomers.
The patent teaches separation of the modified polymer (apparently by selective precipitation during solvent removal) and recognizes no utility for the low molecular weight cleavage fragments (co-products). Further, the greater the extent of chain scission, the less difference there is in molecular weights between the reaction products and the more difficult separation of the modified polymer becomes.